Gravitational Wave Recoil Oscillations of Black Holes: Implications for Unified Models of Active Galactic Nuclei

TL;DR

This paper explores how gravitational wave recoil causes supermassive black holes to oscillate, affecting the observable properties of active galactic nuclei and potentially explaining the scarcity of type 2 quasars.

Contribution

It introduces a model linking gravitational wave recoil to SMBH displacement, impacting unified AGN models and quasar classifications.

Findings

Approximately half of major mergers result in SMBHs displaced beyond the torus for over 30 Myr.

Displacements due to recoil can explain the deficiency of type 2 quasars.

Recoil oscillations influence observable AGN properties.

Abstract

We consider the consequences of gravitational wave recoil for unified models of active galactic nuclei (AGNs). Spatial oscillations of supermassive black holes (SMBHs) around the cores of galaxies following gravitational wave (GW) recoil imply that the SMBHs spend a significant fraction of time off-nucleus, at scales beyond that of the molecular obscuring torus. Assuming reasonable distributions of recoil velocities, we compute the off-core timescale of (intrinsically type-2) quasars. We find that roughly one-half of major mergers result in a SMBH being displaced beyond the torus for a time of 30 Myr or more, comparable to quasar activity timescales. Since major mergers are most strongly affected by GW recoil, our results imply a deficiency of type 2 quasars in comparison to Seyfert 2 galaxies. Other consequences of the recoil oscillations for the observable properties of AGNs are also discussed.